Electrical transmission of light by phase control



May 24,1932. J. HL-HAMMOND, JR" 1,860,341

ELECTRICAL TRANSMISSION OF LIGHT BY PHASE CONTROL 2 Sheets-Sheet 1 JMHWWHOUHHH May 24, 1932.

I J, H. HAMMOND, JR 1 ELECTRICAL TRANSMISSION or LIGHT BY PHASE CONTROL Original Filed J uly 13, 1927 2 Sheet s-Sheet 2 JNVENTOR mm mm nmmouo JR A TORNEY Patented May 24, 1932 UNITED; STATES JOHN mus HAMMOND, .13., or enoucns'rnn, MAssAcnusE'rrs ELECTRICAL TRANSMISSION or menu: IBY PHAsE'coNrnoL Application filed July 18, 1927. Serial No. 205,396. Renewed February 4, 1930.

This invention relates broadly to signal ling systems and more particularly to picture transmission systems and the like.

For thepurpose' of transmission of pictures there are three types of circuits to be considered. The first class is that existing over a telephone or telegraph wire line, a second class circuit is that to be had by radio under good conditions, and the third type of circuit, and that which is most generally found to exist in transatlantic and other long distance work, is a radio circuit wherein static and other disturbances are common and transmission is diflicult.

With circuits of the first and second. class it is possible and very easy to transmit pic tures using modulation of the light impulses. However, with circuits of the third class, so far,' it has been impossible to transmit clear 2 pictures with a modulation system and resort must be had to the make and break system which gives'a icture which is not entirely satisfactory and rather broken up by splashes of static and other disturbances. I

The present invention has for one ofits objects the utilization of shifting of the phase of a transmitted wave in order to control light modulation and thereby be able to transmit a modulated signal over a third class circuit without any interruption or breaks clue tostatic or other interferences.

Another object of this invention is the transmission of electrical modulation without any apparent electrical difi'erence in the transmission itself.v

A further object of the invention is the transmission of intelligence without theuse of a modulated carrier. wave but by-the use of shifting phases. Other objects and uses of the invention will be apparent from the following specification taken in connection with the appended claims. r l I Referring now more particularly to the appended drawillgs-Figxlshows a transmitter for use with the herein described system'of light phase control andFig. 2 represents a receiver for receiving waves transmitted by the apparatus of Fig. 1. g Referring now more particularly to Fig. 1,

11 represents a source of Flight whichmay be varied by any well-known process such as in transmission of pictures by ordinary land,

7 line,12 represents a concentrating lens and 13 represents a photo-electric cell having the elements 14 and 15, the resistance between 5;,

which is adapted to be varied by the light concentrated upon them. Connected in series with the element 15 is the source of potential I 16 shunted by the radio frequency bypass condenser 17. Completing the photo-electric cell circuit is the inductance 18 which is inductive'ly coupled to and controlled by the inductance 53. The thermionic oscillator 22 has its grid 23 connected to the inductance 18 and has in its plate circuit the inductance a 37 and the high potential source 27, the former of which is inductivelycoupled to the in put inductance 18 in the usual manner. I

The'p'iezo controlled oscillator 43 has the piezo crystal 52 connected between the grid 7 44 and the plate 45. Included in the plate circuit'of the oscillator 43, is the high poten-. tial battery 48 and the inductance 49. Ineluded inthe grid circuit is the inductance 50 inductively coupled to said last mentioned inductance, and the inductance 53 which, as was previously stated, is inductively coupled to the inductance 18 and adapted to control thereby-the frequency of oscillation of the oscillator 22. The capacity 51 is shunted 1 across the inductance 53 and is for the purpose of determining the frequencyof the piezo; oscillator.

The output of the oscillator 22 is supplied to the grid 31 of-the thermionic amplifier 3O 35 and the plate circuit of said thermionic amplifier 32 includes the inductance 38 of the oscillation transformer 38-39, the latter mentioned winding of which is the inductance of the antenna circuit which includes the antenna 41, the antenna capacity 40 and thev ground 42. "For heating the filaments 25, 33 and 46 of the thermionic devices 22, 30 and 43 respectively, are provided the low potential batteries 26 and 47. For regu lating the temperature of the filaments 25 and 33' are provided the'rheostats 28 and '34 respectively. 1

Referring now more particularly to Fig.2,v 64 represents' an antenna, 60.and 62 antenna 61 of the input of the vacuum tube detector 76.

Included in the grid circuit of the vacuum tube device 76is the grid leak and grid leak con denser 74. The plate of the thermionic device 76 is coupled through the inductance 87 to half of the split primary of the transformer 85. Inductivelv coupled to the 1nductance 62 is the phase reversal circuit 63, 66

and 67 ,and inductively coupled to the last named inductance 67 is the inductance 68 which is adapted to supply the grid of the thermionic device 77,- provided in the grid circuit of which is the grid leak and the grid leak condenser 75. The output of the device 77 is fed through thesplit half of the primar 84 and through the source of high potential 86 back to the hot cathode. The filaments of the thermionic devices 76 and 77 are connected in series and are heated by energy supplied by a low potential source 78.

The magnetic modulator represented at 71 comprises the inductances 53, 73 and 72, the latter being in the input circuit of the thermionic device 77, and inductance 73 being inductively coupled by means of the inductance 88 to theinductance 87 in the output circuit of the thermionic device 76. Inductance 53 is in the oscillatory circuit of the piezo controlled oscillator 43 which is similar to the oscillator shown in Fig. 1 similar numerals referring to like parts.

Inductively coupled to the primary of the transfonmer is thesecondary 89 which has in its circuit the inductance 91 and the condenser 90. Inductively coupled to the inductance 91 is the inductance 92 of the input circuit of the amplifier 93. The output cir-.

cuit of the amplifier 93 is completed through the inductance 94 and the capacity 97 and in shunt therewith is the switch which is adapted to connect therewith the lamp through suitable non-inductive resistances 98 and 99, a choke 102, and a rheostat 101. Adjacent to the lamp 100 is the screen which 7 is adapted to reflect the light from the lamp 100 and concentrate by means of the prism or lens 103 uponthe eye of the observer 104 or upon the scanning prism or mirror in the usual manner.

Briefly the operation of the apparatus is as follows:- The thermionic oscillator'43 is operated in the-usual and well-known man- .ner to produce a certain frequency and this frequency is held constant by the use of a piezo crystal 52 connected between thegrid and plate circuits as shown. -The output of 6 the oscillator 53 is inductively coupled to the input of the oscillator 22 and un er normal circumstances will contr'ol'the frequency of its oscillation. However, should a light at 11 become greater than the threshhold value of the photo-electric unit 13, a current will be set upin the circuit including the anode and lator 22. Therefore t e oscillator 22will begin to get out of step with the frequency of the oscillator '43. This will cause a transmission through the amplifier 30 which will have practically the same frequency as the normal transmission but will hate a slightly shifting phase. The oscillator 43 ofthe receiver is kept in step and is originally started in step with the oscillator 43 of the transmitter and when the incoming signals in the receiver are in phase with'the local oscillator 43-of the receiver, no result is caused in the circuit '89, 91. The reason for this is as follows. The incoming signals are impressed upon the in ut circuit of the detector 76 and in reverse p ase are also impressed upon the input circuit of the the phase changer 63, 67. The outputs of the two detectors? 6, 77 are fed through the split primary of the transformer 83, 84 and produce upon the secondary 89 a, zero result.

The inductance '88 which is coupled with the detector 77 by means of output of the thermionic detector 76 by means will not effect the inductance 72. The out-- put of the oscillator 43 will therefore have 5 no effect upon the input of the device 77 when theincomingoscillations are in phase with the local oscillator. When, however, the light impulse due to the source of light 11 in Fig. 1 increase above the threshhold value of the device 13, and as a result the characteristics of the oscillator 22 are altered so as to cause a change in the frequency of said oscillator and a corresponding shifting of phase between the oscillation produced by the master oscillator 43 and the oscillator 22, the phase between the incoming signals of the receivcr of Fig. 2 and the oscillator 43 will be corrated out of phase with the oscillations produced by the oscillator 43. Therefore an asymmetric impulse will be created in the wmding 84.- which impulse will-transmit to the circuit 89, 91 and the amplifier circuit impulses corresponding in amount'to the amount of the phase shift in the original transmitter and will produce in the lamp 100, when suitably adjusted by means of the rheostat 101, a light corresponding to the light stimulus at the source 11. 7

When the light stimulus 11 decreases to an respondingly shifted and as a result the core of the magnetic modulator 71v will be satu- 7 amount below the threshhol-d value oftheapparatus 13, the oscillator 43 will regain control of the oscillations of the oscillator 22 and mo resulting energy will be supplied to the circuit 89, 91 of the receiver of Hg. 2. Under this condition the light of Fig. 2 will no longer be stimulated.

It is understood that the invention may be" utilizedfor transmission of messages in code by the simple substitution of a key for the photo-electric device 13 and a sounder or telephone for the light 100 of the receiver of Fig. 2. Other andequally useful application of this device are obvious and the applicant does not Wish to be limited by the, specification, except as covered in the following claims Thus having fully described my invention, what it is desired ,to claim and protect by Letters Patent, is set forth as follows:

1. The method of electricaltransmission of light by phase control, which comprises generating at the receiving station and at the transmltting station a series of waves of a frequency accurate to within a very small degree and in phase with each other, generatin'g at the transmitting station oscillations of a second frequency normally controlled by said first generated frequency, varying the frequency of said last named oscillations by a small amount in accordance with fluctuation in light intensity, transmitting said last generated oscillations, receiving said last generated oscillation, and combining said received oscillations with said locally produced oscillations and producing therefrom an impulse corresponding to the difference in phase between two said series of oscillations.

2. The method of electricaltransmission.

of light by phase control which comprises generating a series of waves of a frequency accurate to within a very small degree, gen-v erating a second frequency normally controlled by said first generated frequency,

varying the last named generated frequency by a small amount in accordance with fluctuation in the light intensity, combining the varied frequency energy with said constant Jfrequency energy so asto produce therefrom an impulse corresponding to the difference in phase between two said frequencies.

3. The process of electrical transmission of light which comprises generating-a series of continuous frequency oscillations, controlling the .frequency of said oscillations to a high degreeofaccuracy, generating a second series of high frequency-continuous oscillations, normally of the same frequency as said first named oscillations, controlling the frequency of said last named oscillations by the frequency of said first named oscillations, amplifying, said last named oscilla-t tions, transmittingsaid amplified oscillations and varying the frequency of said last named oscillations from the frequency of said contuations in light intensity; I 1 a 1 4. Theprocess of electrical transmission of light which comprises generating a series of continuous frequency oscillations, controlhigh degree of accuracy, generating a second trolling oscillations in accordance .withfluc 7 ling the frequency'of said oscillationsto a V series of high frequency oscillations normally of the same frequency as that of said first named oscillations, controlling the frequency of said last named oscillations bythe fre quency of said first named oscillations, varying the-frequency of said last named oscillations from said controlling oscillation in accordance with fluctuations' in light intensity, amplifying said light controlled oscillations,

transmitting said amplified oscillations, re-

ceiving said transmitted light varied'oscillations, providing a series of oscillations of the same frequency as said first named series 1 of oscillations and accurate to a high degree,

detecting said received light varied. oscillations and utilizing gaid detected light aried oscillations for the purpose of preventing said last named accurately controlled oscillations from effecting the detection of said incoming received oscillations when said in coming received oscillations are out of phase with said last mentioned highl accurate oscillations, and utilizing the 'di erential of the detected incoming/oscillations and thedetected light varied oscillations to produce i variations in lightintensity.v

5. In a photo transmission apparatus, an

adapted to be controlled thereby, a photoelectric cell adapted to be controlled by light impulses, said photo-electric cellbein g adapted to vary the frequency of said last men-. tioned-oscillator from the control of said first, mentioned oscillator, and means, for-trans-v mitting'the oscillations of said last named f oscillator, and receiving means comprising means for receiving saldosclllation,'a th1rd oscillator at said receiving station forgencrating a third series ofoscilla-tions-in phase with and, of the same frequency assaidfirst mentioned oscillator and meansforfproducinga light of varying intensityin accordance with the light at said transmitting station, a 7. A device of the character described comprising a transmitter and areceiver, said transmitter. including a high frequency.

piezo controlled oscillator, a high frequency" j the oscillations produced 'bysaid last mentionedoscillator, said receiver including a I fied, and said receiver including means for.

receiving and utilizingthe radiated energy comprising two thermionic amplifiers arranged in push-pull relationship, means for impressing the incoming signals upon both of said thermionic amplifiers so as to produce a zero result under normal conditions, a piezo controlled osclllator having the same frequency as the piezo controlled oscillator of the transmitter and operating directly in phase therewith and adapted to act upon the input of one of said thermionic detectors un-.

der the control of a controlling circuit from the output of the other of said thermionic detectors so that when the received transmission is in phase'with the oscillations .pro-

duced by the local piezo oscillator'the latter will not affect the detector and a zero result will be produced, and an amplifier for amplifying the output of the push-pull detector and a utilization circuit for controlling a current flowing through an illuminating device the intensity of which will be varied in proportion to the intensity of the li ht source acting upon the photo-electric c l of said transmitter. i

8. A device of the character described comprising a transmitter and a receiver, said transmitter includinga high frequency master oscillator, a high frequency thermionic oscillator adapted to be normally controlled thereby, a photo-electric cell adapted to re- 'ceive light variations, connections between said photo-electric cell and said last named oscillator to vary the frequency thereof in accordance with intensity oflight variation, a thermionic amplifier adapted to ampli second master oscillator having the sainefrequencies as the master oscillator of said transmitter and in phase therewith, two ther-' mionic detector devices arranged in pushpull relationship, means for lmpressing upon the input of said push-pull detector the energy receive from said transmittingstw tion, an output circuit for; said push-pull detector so arranged that under normal circumstances no output will result from the transmission, afconnection between the second i masteroscillator and one side of the input of the push-pull detector,- a connection from the other side of the 'push pull dedetector tor for preventing the; latter from effecting the input of said detector, a utilization circuit for utilizing the difierentiat between the frequency of the incoming signal and the fre tector device comprisin tector to the input of the other side in cooperation with the ouput of said second master oscillator, and means whereby when the incoming oscillations are of the same frequency as said local oscillations, said local oscillations will be prevented thereby from effecting the input 0 said push-pull detector and a utilization circuit for utilizing the differential between said oscillations receivedand said oscillations locally generated.

9. A device of the character described comprising a high frequency master controlled oscillator, a high frequency thermionic oscillator adapted-to be normally a controlled thereby, means for varying the frequency of said last mentioned oscillator in accordance with light intensity, a receiving device comprising a push-pull detector system, a local source of oscillations of the same freque'ncy'and in phase withthe master 'oscillator of said'transmitter, a connection between the out ut of said last mentioned os-.

cillator and t e input of one side of said push-pull detector, a connection between'the output ofthe other side of saidpush-pull and the output of said local osc llaquency locally generated.

10. A receiver for photo-electric work comprising a high frequency generator of constant frequency oscillation, a thermionic detwo tector tubes arranged in push-pull fashion,

an output circuit for said push-pull' detector device so arranged that the incoming signals will neutralize each other with respect to the said output circuit, connections between said local oscillator and the input of one of said 7- a metric current to flow in the output of said -detector devices.

electric radio transmission comprising an extremely accuratehigh frequency master oscillation generator, an input circuit for the incoming si als, two thermionic detector devices, a coi in said input circuit, a second coil connected between the grids of the two thermionic devices, aconne'ction between the mid-point of said last mentioned coil and the filaments of the said devices, said first mentioned and said last mentioned coil being in inductive relationship, an output coil the opposite ends of'which are connected to the outut ofeach of said thermionic devices, a"

utilization circuit, a coil in said utilization thermionic de- 11. A device for the reception of photocircuit inductively connected to said output coil, a magnetic modulator comprising an in put coil, an output coil,'and a control coil,

said input-coil being connected with the outut of said master oscillator, said output coil eing connected in the input of one of said thermionic devices a coil'in the output circuit of the other said thermionic devices, a second coil arranged inductively thereto, connections between said last mentioned coil and the control coil of said magnetic modulator, whereby when the incoming signals are in phase with the locally produced oscillations the local generatoroutput of said push-pull detectors.

12. A receiver for radio transmission in photoelectric work comprising an input circuit having an inductance therein, a coil inductively coupled to said inductance, a pushpull detector circuit connected to said coil, an output circuit for said push-pull detector arrangement so arranged that the'signals "received will exactly neutralize each other, a generator of high frequency oscillations of a constant frequency, a magnetic modulator connected tothe outputof said oscillator, a connection between the output of one side of said push-pull detector to said magnetic modulator, and a connection between the input side of the other side of said push-pull detectorand the magnetic modulator, whereby when said. incoming signals are in phase with the local oscillations there will be no result in the output circuit of said detector and that the current supplied to the output circuit will be in proportion to the phase dif- .ference of the received and locally generated oscillations. a

, 13. The method of transmission of intelligence which comprises generating at the receiving station and at the transmitting station a series of waves of a frequency accurate within a small degree other, generating at the transmitting sta- -t1on .a second frequency normally-controlled by said first generated frequency, varying the second frequency by small amounts in accordancewith desiredsignals to be transmitted, transmitting the ener ed frequency, receivin said last generated frequency, and combining said received freq with said locally produced quency oscillations oscillations and producing therefrom an imulse corresponding tothe difference in phase tween said two sentative of the signal being transmitted.

- 14. The. method of transmission of intelligence which comp 'se waves of a frequen accurate within a very small degree, generating oscillations "of a second frequency normally controlled by said first generated frequency,

quency of said last named osc' ations by amounts proportional accordance with de-' combmsired'signals to be t ansmitted, and

will have no effect on the and co-phasal with eachof. last generatseries of oscillations reprevaryin the fre- I of light which comprises generating a series of continuous frequency oscillations, controlling the frequency of said oscillations to a high degree of accuracy, generating a second series of high frequency oscillations normally of the same frequency as that of said first named oscillations, controlling the frequency of said last named oscillations by the frequency ofsaid first named oscillatlons, varying the frequency of said last named oscillations from said controlling oscillation .in ac- Y cordance with fluctuations in light-intensity,

amplifying said light controlled oscillations,

and transmitting said amplified oscillations.

17. The process of receivingenergy transmitted in accordance with the system set forth in claim 16 which includes receiving said transmitted light -varied oscillations,

providing a series of oscillations of the same frequency as said first named series of oscillations and accurate to a high degree, detecting said'received light varied oscillations anduti izing said detected light variedoscilla- .tions for the purpose of preventing said last named accurately controlled oscillations from effecting the detection of said incoming received oscillations ceived oscillations are out of phase with said last mentioned highly accurate oscillations, and utilizing the differential of the detected incoming oscillations and the detected light variedoscillations to'produce variations in light intensity. I

= JOHN HAYS HAMMOND,JR.

generating a series of I when said incoming. re- 

